Fuel cells which generate electric current by controllably combining elemental hydrogen and oxygen are well known. In one form of such a fuel cell, an anodic layer and a cathodic layer are separated by a non-permeable electrolyte formed of a ceramic solid oxide. Such a fuel cell is known in the art as a “solid-oxide fuel cell” (SOFC). It is further known to combine a plurality of such fuel cells into a manifolded structure referred to in the art as a “fuel cell stack” and to provide a partially-oxidized “reformate” fuel to the stack from a hydrocarbon catalytic reformer.
Prior art catalytic partial-oxidizing (POX) reformers typically are operated exothermically by using intake air to partially oxidize hydrocarbon fuel as may be represented by the following equation for a hydrocarbon and air:C7H12+3.5(O2+3.77N2)→6H2+7CO+13.22N2+heat.  (Eq. 1)Prior art reformers typically are operated slightly fuel-lean of stoichiometric to prevent coking of the anodes from decomposition of non-reformed hydrocarbon within the fuel cell stack. Thus some full combustion of hydrocarbon and reformate occurs within the reformer in addition to, and in competition with, the electrochemical combustion of the fuel cell process. Such full combustion is wasteful of fuel and creates additional heat which must be removed from the reformate and/or stack, typically by passing a superabundance of cooling air through the cathode side of the stack.
It is known to produce a reformate containing hydrogen and carbon monoxide by endothermic steam reforming (SR) of hydrocarbon in the presence of water in the so-called “water gas” process, which may be represented by the following equation:C7H12+7H2O+heat→13H2+7CO.  (Eq. 2)Many known fuel cell systems use water in the reforming process, either recovered from the fuel cell exhaust or supplied to the system. In the case of recovered water, a large heat exchanger is required to condense the water, adding mass, cost, and parasitic losses to the system. In the case of supplied water, the water must be filtered and deionized, resulting in added cost, complexity, and maintenance requirements. In addition, for vehicular applications, the water must be stored, transported with the reformer, and periodically replenished.
It is also known to produce a reformate containing hydrogen and carbon monoxide by endothermic reforming of hydrocarbon in the presence of carbon dioxide in the so-called “dry reforming” process, which may be represented by the following equation:C7H12+7CO2+heat→6H2+14CO.  (Eq. 3)
High temperature fuel cells inherently produce a combination of direct current electricity, waste heat, and syngas. The syngas, as used herein, is a mixture of unburned reformate, including hydrogen, carbon monoxide, and nitrogen, as well as combustion products such as carbon dioxide and water. In some prior art fuel cell systems, the syngas is burned in an afterburner, and the heat of combustion is partially recovered by heat exchange in heating incoming air for reforming or for the cathodes, or for both. In other prior art fuel cell systems, a portion of the anode syngas is recycled into the anode inlet to the fuel cell, in conjunction with fresh reformate, to improve the overall fuel efficiency of the fuel cell system.
What is needed in the art is a means for improving still further the fuel efficiency of a hydrocarbon reformer process.
What is also needed in the art is a means for improving the power density of a fuel cell stack.